1. Field of the Invention
The present invention relates to: a method of forming and grafting polymers on carbon nanotubes and the functionalized products produced therefrom; a method of forming stable dispersions of carbon nanotubes and the products produced therefrom; and a method of forming composites from functionalized carbon nanotubes and the composite products produced therefrom.
2. Background
Single-walled carbon nanotube (SWNT) and multi-walled carbon nanotube (MWNT) materials (SWNT and MWNT being collectively referred to herein as “CNT”) exhibit outstanding physical, chemical and mechanical properties, and have been understood to have enormous potential for materials applications. For example, it has been expected that CNT materials should be useful in many different fields including field emission displays, supercapacitors, molecular computers, and ultrahigh strength materials. However, most such applications employing the unique electronic, thermal, optical, and mechanical properties of CNT require that the CNT material be in individual (unbundled) form and in high purity. Unfortunately, as-prepared CNT products contain significant impurities, many of which consist of or include metal catalyst particles and amorphous carbon. Moreover, the individual nanotube elements of the CNT products pack together to form bundles that aggregate into tangled, essentially unusable, networks due to strong van der Waals attraction.
To date, a number of purification methods have been attempted. They can be categorized as acid oxidation, gas oxidation, filtration, chromatography, microwave treatment, and organic functionalization. By using these methods, most of the metal catalyst particles and the amorphous carbon in raw CNT materials can be removed; leaving rather purified CNT in different yields. The disadvantages of these purification methods are that multiple treatment steps are needed and/or only a small quantity (e.g., about 5 mg) of CNT is purified each time. Furthermore, as seen by transmission electron microscopy (TEM) imaging, the purified CNT product is still in the form of big bundles which will not dissolve in any current solvents.
Although some progress has been made toward the solubilization of CNT in both organic and aqueous media, the results have thus far been inadequate. Dissolution in organic solvents has been reported with bare CNT fragments and with chemically modified CNT. Dissolution in water, which is more important because of potential biomedical applications and biophysical processing schemes, has been facilitated by surfactants and polymers, by polymer wrapping, and by chemical modification. In most of these studies, however, the extent to which the suspended materials exist as individual tubes or small bundles of tubes has not been reported. Furthermore, tube aggregation in solution has not been well quantified.